This invention relates to a new process for the preparation of plastics containing thermoplastic polyurethanes ("TPU"). It is known from U.S. Pat. No. 3,214,411 that the starting compounds for TPU, particularly isocyanates, chain extenders, and polyols, can be transferred from a mixer to a belt to form a polyurethane. The polyurethane obtained is subsequently size-reduced and homogenized in extruders to form granulates. This process is known as "refining".
It is also known that preformed TPU can be mixed together with other components, such as glass fibers, polycarbonates, or other polymers (such as ABS, for example), in an extruder and the resultant blend subsequently granulated. This process is known as compounding.
In addition, German Offenlegungsschrift 2,854,406 describes a process for preparing a thermoplastic material in which fibrous reinforcing materials and polar polymers are added to the polyurethane-forming components before or after preparation of a thermoplastic polyurethane in a twin-screw extruder. The disadvantage of the known compounding or refining process is that the thermoplastic polyurethane elastomers are damaged by high friction and exposure to high temperatures. This damage leads to a reduction in tensile strength, impact strength at low temperatures, and viscosity. Partly crystalline products lose their crystallinity, leading to lower solidification rates. The damage caused by friction is proportional to the viscosity of the starting material, the degree of degradation not being sufficiently controllable.
The object of the present invention was to provide an improved process for the preparation of plastics containing thermoplastic polyurethanes. More particularly, the purpose of the invention was to improve compounding or refining.